Contents

Group

Description

The KraftTech Power Sander is a light duty orbital sander. It is used to sand small to medium sized wooden items and accepts various grits of sandpaper. The sanding pad oscillates in a small circle, constantly moving even when the user isn't, allowing for much faster sanding than with just paper.

Specifications

This sander was most likely designed to meet these customer specifications:

Fast sanding

Able to remove material quickly

Comfortable to hold

Doesn't hurt to use even with constant vibration against hand

Removes dust from surface

Reduces possible particulate in air

AC Power Connection

Can be plugged into wall outlet instead of battery

In addition to customer requests, engineering specifications might have also been provided:

Accepts 60Hz 120VAC

Runs on standard wall current

Uses standard 1/4 sheets of sandpaper

Won't require hard to find consumables

Minimal internal losses

More efficient power usage - correlates to Fast Sanding

Minimal vibration felt by user

Similar to Comfortable to hold, this also is a part of mechanical efficiency by requiring that more power go to the movement of the sanding plate than the user

Parts

List of parts

Table 1: Power Sander Component List

Part #

Part Name

Category

Function

Material

Picture

Model

1

Power Cord

Input

Provides power to the Power Sander

Insulated Wires

2

Switch

Input

Allows user to toggle power on and off

Plastic with metal contacts

3

Feathers

Input

Provides power to the motor

Carbon

4

Motor

Input

Spins the driveshaft

Copper, Steel

5

Sanding Platform

Output

Performs the base for the sanding function of the tool

Plastic/rubber

6

Fan

Output

Moves dust from surface into the dust collector, cools the motor

Plastic

7

Dust Director

Output

Directs the dust into the dust collector

Plastic

8

Offset Weight

Motor Conversion

Provides vibration and non-uniform motion within Power Sander

Steel

9

Bearings

Support Element

Allow smooth, rotational motion

Steel

10

Flexible Legs

Structural Component

Attaches the Sanding Platform to the body, allowing for a balance of rigidity and a small amount of motion

ABS Plastic

11

Casing

Structural Component

Shields the user from electrical contact, gives the device its shape, provides support to the entire tool

ABS Plastic

12

Sandpaper Clips

Other Components

Hold the sandpaper in place

Steel

Details on Modeled Parts

Table 2.1: Offset Weight

1

What decisions were made in the design of this component/module?

The dimensions of this part directly control the vast majority of vibration in the sander, so the designer had to decide the radius of rotation for the pad. The weight and moment of this part also directly correspond to the possible weight and sanding friction that the pad can provide.

2

What are the critical features and dimensions?

The most critical aspect of this part is the distance that the hub is offset from the input shaft and its relation to the weight distribution of the part. The weight distribution is designed to be exactly opposite to the weight of the sanding pad when it is moving around in the offset circle, and any imbalance of these two moments would cause the entire sander to vibrate much more and cause more wear on internal components.

3

What kind of loading do we expect to be on the component?

This part will take the output torque and power from the motor and push the sanding pad around. The offset hub will be inside the bearing on the pad and will take all the lateral forces from the sandpaper against the surface and any other resistances to the motion. The offset weight will exert a large force in the outward radial direction in the opposite direction of the force from the sanding pad, hopefully with the same magnitude.

4

What measures can we use to evaluate performance?

The vibration of the sander body and motor can be measured, where less vibration shows better performance of this part. This is similar to balancing a tire, and a similar measurement device can be used to show what side needs more weight and how much.

Table 2.2: Bearing

1

What Decisions were made in the design of this component/module?

When designing this bearing, the inner diameter, outer diameter, and thickness had to be decided on. The other main factor that varies between bearings is the resistance to rotation between the different rings. That probably wasn't a big decision in choosing a bearing because the sander is made to be as cheap as possible.

2

What are the critical features and dimensions?

The critical dimensions are the inner diameter, the outer diameter, and the thickness. The critical feature is the ease of rotation between the inner and outer walls of the bearing.

3

What kind of loading do we expect to be on the component?

The loads applied to this bearing will be in the form of rotation between the inside and the outside of the bearing. There will also be forces applied outward from the inner part of the bearing because shaft entering the bearing is offset.

4

What measures can we use to evaluate performance?

To measure the performance of the bearing a shaft can be placed in the bearing, spun, and then the number of rotations before the shaft stops spinning will quantify the performance. The more rotations after the load is released, the higher the quality of the bearing.

Table 2.3: Sanding Platform

1

What Decisions were made in the design of this component/module?

The size, material of the top part and the material of the pad on the bottom.

2

What are the critical features and dimensions?

The critical dimensions are that the part that holds the bearing in the middle isn't too tall and that the holes for the flexible legs to be screwed in are the right distance apart. The overall size is also a critical dimension because it shouldn't extend past the rest of the body of the sander so that the whole tool is one compact unit. A critical feature is that the bottom surface must be soft enough that when pressure is applied, the sand paper provide a smooth sanding of the surface and not scratch the surface.

3

What kind of loading do we expect to be on the component?

The sanding platform will undergo lots of vibrations as it is jolted around from side to side to perform the sanding task. There will also be a force applied to the bottom of the sanding platform as pressure is applied while sanding objects.

4

What measures can we use to evaluate performance?

The performance of this part is directly related to the performance of most other parts of the tool. The vibrations are a result of the motor, flexible legs, and offset weight. The softness of the bottom can be measured by sanding corners and evaluating how clean the sanding finish is.

Table 2.4: Flexible Legs

1

What Decisions were made in the design of this component/module?

Due to the nature of the legs and their function within the sander, the strength of the material and rigidity of the design were primary decisions for the design. The weight and cost of the material entered the decision-making process because of the sander's purpose and desired cost.

2

What are the critical features and dimensions?

The size of the "legs" is ultimately constrained to the requirement that the device fit in one hand. The most critical features of the legs is that each can withstand the continuous vibration, the stress due to the force applied through the tool against the surface, and the balance between structural support and stability, and its allowance and absorption of small movement and vibration. The legs are required to meet dimensional specification such that they are the appropriate length to attach the sanding platform to the device and are the correct width to allow for proper fitting within the plastic casing of the sander.

3

What kind of loading do we expect to be on the component?

This part ultimately receives the applied force and distributes it to the sanding pad. There are two sets of the flexible legs, totaling four contact points to transfer the load primarily along the axis of the legs' cylinders. The motion of the sander along the surface also creates a lateral force, though of a lesser value. In addition, these ABS plastic legs must be capable of adequately supporting the sanding pad while undergoing the constant vibration.

4

What measures can we use to evaluate performance?

Due to the inexpensive nature of the flexible legs, it is worthwhile to experimentally test the strength of the legs under "normal" conditions, assisting in measuring the device's probable lifetime. Due to a variance in the user base and thus the user's applied force, a maximum downward force can be applied to acquire the yield strength. The balance of strength, rigidity, and vibrational dampening could also be measured by analyzing the change in vibration between the surface and the user's hand. In all, a failed or collapsed leg would reflect failure and poor performance of the flexible legs.